Absence of both IL-7 and IL-15 severely impairs the development of CD8 T cell response against Toxoplasma gondii.

Bhadra R, Guan H, Khan IA - PLoS ONE (2010)

Bottom Line:
However, attenuated maturation and decreased effector functions in these mice are essentially downstream consequences of reduced number of antigen-specific CD8(+) T cells.Interestingly, the absence of both cytokines did not impair initial CD8(+) T cell generation but affected their survival and differentiation into memory phenotype IL-7Ralpha(hi) cells.To the best of our knowledge this synergism between IL-7 and IL-15 in generating an optimal CD8(+) T cell immunity against intracellular parasite or any other infectious disease model has not been previously reported.

ABSTRACTCD8(+) T cells play an essential role in the protection against both acute as well as chronic Toxoplasma gondii infection. Although the role of IL-15 has been reported to be important for the development of long-term CD8(+) T cell immunity against the pathogen, the simultaneous roles played by both IL-15 and related gamma-chain family cytokine IL-7 in the generation of this response during acute phase of infection has not been described. We demonstrate that while lack of IL-7 or IL-15 alone has minimal impact on splenic CD8(+) T cell maturation or effector function development during acute Toxoplasmosis, absence of both IL-7 and IL-15 only in the context of infection severely down-regulates the development of a potent CD8(+) T cell response. This impairment is characterized by reduction in CD44 expression, IFN-gamma production, proliferation and cytotoxicity. However, attenuated maturation and decreased effector functions in these mice are essentially downstream consequences of reduced number of antigen-specific CD8(+) T cells. Interestingly, the absence of both cytokines did not impair initial CD8(+) T cell generation but affected their survival and differentiation into memory phenotype IL-7Ralpha(hi) cells. Significantly lack of both cytokines severely affected expression of Bcl-2, an anti-apoptotic protein, but minimally affected proliferation. The overarching role played by these cytokines in eliciting a potent CD8(+) T cell immunity against T. gondii infection is further evidenced by poor survival and high parasite burden in anti IL-7 treated IL-15(-/-) mice. These studies demonstrate that the two cytokines, IL-7 and IL-15, are exclusively important for the development of protective CD8(+) T cell immune response against T. gondii. To the best of our knowledge this synergism between IL-7 and IL-15 in generating an optimal CD8(+) T cell immunity against intracellular parasite or any other infectious disease model has not been previously reported.

pone-0010842-g005: Bcl-2 and IL-7Rα are downregulated in BrdU+CD8+ T cells from IL-7 depleted KO mice.Splenocytes from BrdU injected antibody or saline treated KO mice were harvested at day 6 and day 14 p.i. The cells were stained for CD8β, CD127, Bcl-2 and BrdU as described in Materials and Methods. A, The Bcl-2 vs. CD127 density-contour plots depicted on the top panel are gated on CD8+Brdu+ T cells (top left panel) and CD8+BrdU− T cells (top right panel). B–D, Bcl-2 MFI of CD8+BrdU+ T cells (B), CD8+BrdU+CD127hiBcl2+ T cells (C) and CD8+BrdU+CD127hiBcl2hi T cells (D) are presented as bar graphs in the lower panel. The experiment was performed twice with similar results. The data is representative of one of two similar experiments with 3–4 mice per group.

Mentions:
Animal studies were carried out in agreement with Institutional Animal Care and Use Committee approved guidelines at George Washington University Medical Center. 6 to 8 week old female IL-15−/− mice (Taconic Farms) and C57BL/6 mice (NCI) were infected per-orally with 10 cysts of ME49 strain (Figure. 1–6) of T. gondii. CD8+ T cell responses were evaluated at day 14 post-infection (p.i.). Anti IL-7 antibody (M25) was a kind gift from Amgen. The antibody was injected into wild-type or IL-15−/− i.p. (intraperitoneally) at 0.5 mg per mouse at 3-day intervals. The treatment was initiated one day before infection and continued till termination of experiment. Control mice were injected with equal volume of saline. For some experiments, IL-15−/− and anti IL-7 treated IL-15−/− animals were infected i.p. with 1×106 cps1-1 parasites (Figure. 7) and CD8+ T cell responses were evaluated at day 14 p.i..

pone-0010842-g005: Bcl-2 and IL-7Rα are downregulated in BrdU+CD8+ T cells from IL-7 depleted KO mice.Splenocytes from BrdU injected antibody or saline treated KO mice were harvested at day 6 and day 14 p.i. The cells were stained for CD8β, CD127, Bcl-2 and BrdU as described in Materials and Methods. A, The Bcl-2 vs. CD127 density-contour plots depicted on the top panel are gated on CD8+Brdu+ T cells (top left panel) and CD8+BrdU− T cells (top right panel). B–D, Bcl-2 MFI of CD8+BrdU+ T cells (B), CD8+BrdU+CD127hiBcl2+ T cells (C) and CD8+BrdU+CD127hiBcl2hi T cells (D) are presented as bar graphs in the lower panel. The experiment was performed twice with similar results. The data is representative of one of two similar experiments with 3–4 mice per group.

Mentions:
Animal studies were carried out in agreement with Institutional Animal Care and Use Committee approved guidelines at George Washington University Medical Center. 6 to 8 week old female IL-15−/− mice (Taconic Farms) and C57BL/6 mice (NCI) were infected per-orally with 10 cysts of ME49 strain (Figure. 1–6) of T. gondii. CD8+ T cell responses were evaluated at day 14 post-infection (p.i.). Anti IL-7 antibody (M25) was a kind gift from Amgen. The antibody was injected into wild-type or IL-15−/− i.p. (intraperitoneally) at 0.5 mg per mouse at 3-day intervals. The treatment was initiated one day before infection and continued till termination of experiment. Control mice were injected with equal volume of saline. For some experiments, IL-15−/− and anti IL-7 treated IL-15−/− animals were infected i.p. with 1×106 cps1-1 parasites (Figure. 7) and CD8+ T cell responses were evaluated at day 14 p.i..

Bottom Line:
However, attenuated maturation and decreased effector functions in these mice are essentially downstream consequences of reduced number of antigen-specific CD8(+) T cells.Interestingly, the absence of both cytokines did not impair initial CD8(+) T cell generation but affected their survival and differentiation into memory phenotype IL-7Ralpha(hi) cells.To the best of our knowledge this synergism between IL-7 and IL-15 in generating an optimal CD8(+) T cell immunity against intracellular parasite or any other infectious disease model has not been previously reported.

ABSTRACTCD8(+) T cells play an essential role in the protection against both acute as well as chronic Toxoplasma gondii infection. Although the role of IL-15 has been reported to be important for the development of long-term CD8(+) T cell immunity against the pathogen, the simultaneous roles played by both IL-15 and related gamma-chain family cytokine IL-7 in the generation of this response during acute phase of infection has not been described. We demonstrate that while lack of IL-7 or IL-15 alone has minimal impact on splenic CD8(+) T cell maturation or effector function development during acute Toxoplasmosis, absence of both IL-7 and IL-15 only in the context of infection severely down-regulates the development of a potent CD8(+) T cell response. This impairment is characterized by reduction in CD44 expression, IFN-gamma production, proliferation and cytotoxicity. However, attenuated maturation and decreased effector functions in these mice are essentially downstream consequences of reduced number of antigen-specific CD8(+) T cells. Interestingly, the absence of both cytokines did not impair initial CD8(+) T cell generation but affected their survival and differentiation into memory phenotype IL-7Ralpha(hi) cells. Significantly lack of both cytokines severely affected expression of Bcl-2, an anti-apoptotic protein, but minimally affected proliferation. The overarching role played by these cytokines in eliciting a potent CD8(+) T cell immunity against T. gondii infection is further evidenced by poor survival and high parasite burden in anti IL-7 treated IL-15(-/-) mice. These studies demonstrate that the two cytokines, IL-7 and IL-15, are exclusively important for the development of protective CD8(+) T cell immune response against T. gondii. To the best of our knowledge this synergism between IL-7 and IL-15 in generating an optimal CD8(+) T cell immunity against intracellular parasite or any other infectious disease model has not been previously reported.